The present invention is directed towards a method for monitoring the received pulses of a pulse-code modulated data transmission, within a predeterminable pulse distortion tolerance zone.
Methods are known which solve this problem by repeated sampling of the received pulses, followed by a majority decision in favor of one of the possible states "0", "1", as well as a decision zone for "suppressed pulse" error recognition. Other methods are known which utilize time integrated pulse evaluation, followed by a majority decision concerning the state of the pulse.
Both of these known methods involve increased technical demands and suffer from the disadvantage that pulse level changes with intervals which are short by comparison with the theoretical pulse length cannot be utilized for monitoring the signal quality. These disadvantages exist especially in those transmission systems which are meant to ensure a very small read-out error probability even when the transmission path suffers from heavy interference.
As is well known, the efficiency of any protection against non-recognizably wrong message evaluation depends to a high degree on the properties of the signal quality control.
The primary object of the present invention is to avoid the disadvantages of known methods. To this end, the distortion zone of the received pulses of the pulse-code modulated message is subdivided into two consecutive time zones. During the first of these zones (which extends around the theoretical instant of the expected pulse edge of the received message), a check is made to determine whether no more than one pulse edge has arrived during the first zone. If more than one edge arrives during this time zone, an error-recognition mark is set. An error-recognition mark is also set if during the supplementary second time zone only one pulse edge has arrived.
The relative percentages of the two time zones, whose sum equals the desired pulse length of the transmitted signal, are selectable in steps and adaptable to requirements as regards transmission reliability efficiency and quality of the transmission path.